It is well known to use medical imaging techniques to obtain imaging data that is representative of anatomical structures within the body of a patient or other subject. Volumetric imaging data may, for example, be obtained by the acquisition of a series of two-dimensional slices (usually axial), which may be combined to form a three-dimensional array of voxels.
Volumetric imaging modalities may comprise, for example, computed tomography (CT), cone-beam computed tomography (CB-CT), magnetic resonance (MR) or ultrasound. In a CT data set, for example, each voxel usually has an associated intensity, measured in Hounsfield Units, which represents the attenuation of X-ray radiation by the respective, corresponding measurement volume.
Medical imaging data may be specific to a particular patient, and to a particular scan of that patient.
Medical imaging data can be in a variety of forms and can include any suitable data obtained from measurements by a medical imaging modality. Medical imaging data may be data that can be rendered, or otherwise processed, to obtain an image of at least part of a subject.
A virtual anatomy provides a representation of the location of anatomical features and may, for example, comprise a synthetic, non-patient-specific representation of generic human anatomy in three dimensions. A virtual anatomy may provide features such as the identification of organs and other anatomical structures. Anatomical structures (for example, the liver or other organs) may be named in the virtual anatomy. Anatomical structures may be given a shape and a position within the body.
Volumetric virtual anatomy data may comprise a set of voxels, for example a three-dimensional array of voxels, that may be similar to the three-dimensional array of voxels obtained through a medical imaging scan. For example, each voxel in the volumetric virtual anatomy data may have an associated intensity value. In volumetric virtual anatomy data, voxels may be assigned to anatomical structures within the human body, for example to provide a generic representation of the human body in which anatomical structures are segmented.
It is known to map volumetric patient data comprising an array of voxels to volumetric virtual anatomy data comprising an array of voxels, for example using similar registration techniques to those that may be used to register one set of volumetric patient data to another set of volumetric patient data. One approach to mapping volumetric patient data to volumetric virtual anatomy data is to use image similarity-based registration techniques, for example optimization based on mutual information. Image-based registration techniques may be computationally intensive, and therefore may be slow.
Other types of virtual anatomy data are known, in addition to volumetric virtual anatomy data comprising an array of voxels. For example, model-based virtual anatomy data is known in which anatomical structures are represented by models, for example surfaces or regions in three-dimensional space, rather than by labeled arrays of voxels.